NAME
wikifs, wikipost – wiki file system

SYNOPSIS
wikifs [ –DM ] [ –a announce ]... [ –m mtpt ] [ –p perm ] [ –s service ] dir

ip/httpd/wikipost [–b inbuf] [–d domain] [–r remoteip] [–w webroot] [–N netdir] method version uri [search]

DESCRIPTION
A wiki is a web server that facilitates easy editing of the pages it contains. Wikifs presents a wiki in two forms: as web pages to be served via httpd(8) and as text files to be viewed via the acme(1) wiki client (see /acme/wiki/guide).

Wikifs presents a file system interface to the wiki data stored in dir. By default, wikifs mounts itself at /mnt/wiki; the –m flag specifies a different mount point, and the –M flag causes wikifs not to mount at all. Wikifs also announces 9P network services on the addresses given as arguments to –a options. If the –s option is given, wikifs will post a service file descriptor in /srv/service with permission perm (default 600). The –D flag causes a transcript of the 9P conversation to be written to standard error.

The wiki holds both the current pages and also all versions of all pages that have ever existed. All pages have time stamps associated with them. When a user wants to edit a page, he reads the current page from the wiki, noting the time stamp on the page. When a user writes changes to a page, he includes the time stamp of the page he started with. If the page has been updated by someone else while he was editing, the write will fail. This is called a ``conflicting write.'' The submission is still saved in the history, so that the user can compare the page he submitted with the changes that were made while he was editing.

Each version of each page is described by a text file containing one or more metadata lines followed by the page contents. The metadata lines begin with a capital letter specifying the type of data. Currently the metadata types are:
D     The date this page was written, in decimal seconds since the epoch.
A     The author of this version of the page. Typically the rest of the line takes the form name ip–address.
X     This page's contents were submitted but rejected due to a conflicting write.

After the metadata comes the actual page contents; each line of page contents is prefixed with a # character.

The directory dir/d contains all the wiki data. Typically it is world–writable so that wikifs can run as none. Each page on the wiki has a unique sequence number n; for each page, the d directory contains three files n, n.hist, and L.n. The file n holds the current version of the page: the first line of n is the page title, followed by page metadata and contents as described above. The append–only file n.hist holds the history of the page. The first line of n.hist is the title of the page. The rest of the file is the metadata and contents of every version of the page that has been submitted to the wiki. L.n is a lock file for the page: it must be held while reading or writing n and n.hist. The lock files allow multiple instances of wikifs to coexist peacefully. Finally, the map file (with associated lock L.map) provides a mapping from sequence numbers to to page titles. Each map line is a decimal n, a single space, and then the title. Since titles are presented as names by wikifs, they cannot contain slashes.

Wikifs presents a three–level file system. The top level contains per–page directories named by the page titles with spaces turned into underscores. Each page also has a number associated with it (see the discussion of the wiki data files below). The number corresponding to a page may also be used to access it, although directory listings will always present the title. The new file is used to add new or revised pages to the wiki: writes to the file should be in the usual textual format: a title line, metadata lines, and page contents. Once all the contents have been written, a final zero–length message should be written to mark the end of the page. This last write will return an error if a conflicting write has occurred. After writing the file, the client may read from new to obtain the canonical title for the page, as presented by the file system.

The page directories contain subdirectories representing the history of the page, named by the decimal time stamp corresponding to each version. In addition to these history directories, the page directories contain the following files:
current
The current raw data file for the page.
diff.html
A web page listing the contents of every version of the page that has ever appeared on the wiki. The text is grey by default: differences between versions appear in black.
edit.html
A web form for editing the the current version of the page.
history.html
A web page listing the time stamps of the historical versions of the page. Each time stamp links to a page showing just that version.
history.txt
A textual formatting of the history. Each time stamp is prefixed with the name of the directory corresponding to that version.
index.html
An HTML formatting of the current version of the page.
index.txt
A textual formatting of the current version of the page.
werror.html
An HTML error page to be returned by wikipost on conflicting writes.

The HTML files are generated from the templates with the same names in dir, except that index.html and index.txt are generated from the templates page.html and page.txt.

The history directories are similar to the page directories but only contain current, index.html, and index.txt. This index.html and index.txt are generated from the templates oldpage.html and oldpage.txt.

The httpd(8) helper program wikipost is used to process editing requests posted to the web server by users. It expects the posted form to contain these (usually hidden) fields: TITLE, the title of the page; VERSION, the time stamp of the page that is being edited; service, the service name associated with this wiki (wikipost looks for /srv/wiki.service); and base, the base for wiki URLs in the response.

After mounting the wiki, wikipost writes a page update request to /mnt/wiki/new and then returns the contents of one HTML file in /mnt/wiki/title. If the write succeeds, wikipost returns index.html. if the write fails due to a conflicting write, wikipost returns werror.html.

EXAMPLE
The Plan 9 wiki at Bell Labs is started by running:
wikifs –p 666 –s wiki.plan9 –a tcp!*!wiki /sys/lib/wiki

The wiki is mounted for httpd(8) by an entry in /lib/namespace.httpd:
# wiki
mount –b #s/wiki.plan9 /usr/web/wiki/plan9
Notice that the wiki service was explicitly posted with mode 666 so that httpd (running as none) would be able to mount it.

In the Plan 9 distribution, the directory /sys/lib/wiki contains sample files similar to those used to start the current Plan 9 wiki.

SOURCE
/sys/src/cmd/wikifs
/sys/src/cmd/ip/httpd/wikipost.c

SEE ALSO
The original wiki, http://c2.com/cgi/wiki?WikiWikiWeb
/acme/wiki/guide
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